1. Chapter 5 Notes

2.  The atomic mass of an element is a weighted average mass of the atoms found in nature.  If you were to mass an oxygen atom, would it weigh 15.9994 amu?  NO! 15.999 amu – THIS IS ONLY AN AVERAGE OF ALL THE ISOTOPES OF OXYGEN 16 O, 17 O, 18 O

3. The relative abundance of each isotope of an element determines its atomic mass. Naturally occurring isotope Fractional abundance Mass (amu) 11 C 011.011430 12 C 0.98912.000000 13 C 0.01113.003355 14 C 014.003241

4.  Three isotopes of oxygen occur in nature: oxygen-16, oxygen-17, and oxygen-18. The atomic mass of oxygen is 15.9994 because oxygen-16 is the most abundant.

5. QUESTION  If element Z has two naturally occurring isotopes: Z-20 and Z-22 and the atomic mass of Z is 21.5 amu  Which isotope occurs most often in nature?  Z-22  the relative abundance of each isotope in nature is one Z-20 to two Z-22.

6.  Thallium has two isotopes, thallium-203 and thallium-205. Thallium’s atomic number is 81 and its atomic mass is 204.38 amu.  So, is there more Thallium-203 or Thallium- 205?  There is more Thallium-205 found in nature.  Atoms of both isotopes have 81 protons. Thallium-205 atoms have more neutrons.

7.  A sample of oxygen contains three naturally occurring isotopes:

8. The relative abundances and atomic masses are:  99.7759% (mass = 15.995 amu)  0.037% (mass = 16.995 amu)  0.204% (mass = 17.999 amu)  Calculate the average atomic mass of the oxygen.

9.  (percent x mass) + (percent x mass) and so on….  0.99759(15.99491) +  0.00037(16.99913) +  0.00204(17.99916) =  15.999 amu

10. Radioactivity (Ch 25)

11.  An alpha particle (radiation) is a helium nucleus.

12.  A beta particle (radiation) is an electron.

13. Gamma Radiation  Gamma radiation is high-frequency electromagnetic radiation. Gamma radiation has no mass or charge so there is no change in the atomic number caused by the emission of gamma radiation.  Nuclear equations are balanced.

14. Complete these nuclear equations.